Machine-tool spindle



June 27, 1939- F. TURRETTINI 2,164,129

MACHINE-TOOL SPINDLE Filed June 16, 1958 Ji an 3%:

Z77 rev/ r Patented June 27, 1939 UNITED STATES PATENT OFFICEMACHINE-TOOL SPINDLE Fernand Turrettini, Bellevue-Geneva,

Switzer- Application June 16, 1938, Serial No. 214,121 In SwitzerlandMarch 31, 1938 4 Claims.

The present invention relates to tool or work spindles of milling,grinding, polishing and like machine-tools.

In usual tool spindles of such machine-tools,

.1 the nose of the spindle is situated at a certain distance from athrust collar of the spindle, by means of which the spindle bearsagainst the spindle housing. When the spindle rotates, it is heated andthe portion of it situated between the nose and the thrust collar issubjected to an expansion which produces a displacement of the nose ofthe spindle and accordingly of the tool or of the work piece carried bythe nose. This displacement, which can attain the order of one 1.1 tenthof one millimeter and will vary during the operation of the spindle withthe variations of temperature of the spindle bearings, can becomeextremely inconvenient,particularly when grinding profiled work, such asscrew threads, and can produce deformation of the generated profile orloss of relative position between the work pieces and the tool in caseof series work including a plurality of operations, as for exampleseparate rough grinding and finishing of a thread. In order to avoidthese inconveniences it has been necessary to let the spindle run idlefor a certain time, to bring it to working temperature before startingactual grinding.

Spindle mountings have already been proposed to temperature rise, bymaking the nose of the spindle itself bear against a thrust bearing. Butin this case the spindle and the thrust bearing have an annularcontacting surface of large diameter which is difiicult to obtainperfectly straight and perpendicular to the axis of the spindle, whichis necessary in order to realize a. perfectly true running of the tool.Furthermore, large thrust surfaces result in high surface speeds withcorresponding temperature rise and rapid wear.

It has also been proposed to make the free 'end of the spindle nose bearagainst an axial abutment for preventing displacement of the tool owingto heat expansion. But in this case the 5 replacement of the tool isdiflicult, since the axial abutment must be removed each time the toolhas to be changed. The object of the present invention is the provisionof a tool spindle which avoids the above mentioned drawbacks and securesmaximum advantages with regard to permanent correct tool position,accuracy of the thrust surfaces, and protection of these surfaces frombeing damaged by grit and cooling medium.

According to the invention the end of the which prevent a displacementof the tool owing 7 spindle carrying the tool is provided with aninternal thrust surface bearing against one end of a rod disposedaccording to the axis of the spindle and having its other end bearingagainst a portion of the spindle frame, the said rod consisting ofmaterial which is nonexpansible or has a small coefficient of thermalexpansion. For example, this rod can be made of a metal alloy which isknown as. Invar.

In the accompanying drawing,

Figure 1 is an axial section of a tool spindle assembly of a grindingmachine.

Figure 2 is a modification of a detail.

The spindle I comprises a body portion I a. and a nose portion lbforming a disk which carries the II grinding wheel 2. The spindle isprovided with a conical journal 3 and with a cylindrical journal I, thefirst one turning in a conical bushing 5 and the second one in acylindrical bushing B mounted in the spindle bearing 1 of the headstick.A spring 8 is placed between the fixed bushing 5 and a thrust ballbearing 9 adjoining the driving pulley l0 secured to the spindle; thisspring constantly tends to push the spindle towards the right in thefigure. The nose of the spindle carries. a screw H the inner end ofwhich forms a small plane surface [2 which bears against the plane endof a rod l3 extending axially within the hollow spindle. The other endof the rod I3 bears against the end 16 of a micrometer screw l4 carriedby the spindle bearing and forming a fixed abutment which is adjustablerelative to the hearing. The rod I3 is made of material having a verysmall coeflicient of thermal expansion, as for instance Invar. 7

Since the rod I 3 is of nonexpansible, or very llttleexpansible metal,it is evident that the position of the grinding wheel does not varyrelatively to the abutment l6 carried by a fixed part of the machine.The grinding wheel accordingly has a a constant position, independentlyof the temperature of the bushings 5 and 6 of the spindle I.

It must however be noticed that the metals known as nonexpansible andgenerally constituted by ferrous alloys with about 36% of nickel. have acoeflicient of thermal expansion which is not exactly zero. The actualcoefiicient can be positive or negative and reach a value of 1.10- up to2.10 per degree centigrade; the coeflicient of Invar is positive.

To take into account the small thermal expanslon of the rod l3, itsthrust face acting on the surface l2 of the screw II is not to be placedexactly in the medium plane of the wheel 2, but at a distance L1 ofsame.

There is L=length .of the non expansible rod l3, a=actual expansioncoeiilcient of the rod ll, t=mean temperature of the rod I! over roomtemperature. Ll=distance between the thrust face I2 and the medium planell of the wheel 2, 1=thermal expansion coeiilcient of the hub is of thewheel, t1=mean temperature of the hub I over room temperature,

A=distance between the medium plane it of the wheel and fixed thrustsurface it, dA=variation of the distance A due to thermal expansion,which is obtained according to the equation:

The sign is valid for an arrangement according to the drawing and allowsto bring dA down to zero when :18 positive. The mean temperatures t andt1 depending on the relative dimensions of the corresponding members andof the cooling conditions, these values will be determined by practicaltests; these latter accordingly will ilx the displacement Ll which isrequired for obtaining perfect compensation.

Should the expansion coeillcient of the rod ll be small but negative,then the thrust face I2 must be located at the right of the medium planell of the wheel, and the above formula will be written:

In each case the ooeiilcient a is to be introduced with its sign; forusual designs using steel spindles, the value of a1 is about ll,5.l-'per degree centrigrade.

The portion of the spindle I adjacent the grinding wheel having analmost constant position relatively to the fixed parts of the machine,such as the bearings I, 1, it is possible to form this bearing with aconical bore so as to be able to adjust the thickness of the lubricatingoil illm between the bearing surfaces by means of the micrometer screwll provided with a graduated drum Ila. This drum can carry a scale whichdirectly indicates the thickness of the oil film. In this way, it is notnecessary to provide a split hearing which is ordinarily used forspindles to adjust the play by its elastic deformation. The accuracy ofguiding obtained with a rigid bearing as shown in the drawing is muchbetter than with an elastic split bearing, because it is never possibleto obtain a perfect iit between the spindle and a split bearing.

The end of the rod 13 bearing against the micrometer screw it can beformed by a piece of hard metal I! such as tungsten carbide or chromium,as is shown in Fig. 2. I

It is obvious that the same principle of invention can be applied to agrinding wheel journaled between two bearings instead of being overhung,as shown. Furthermore, the invention can not only be applied to toolspindles, but also to work carrying spindles, as for example in the caseof a thread cutting lathe.

I claim:

1. A machine-tool spindle having a portion thereof remaining in aconstant transverse plane irrespective of thermal expansion due toheating of the spindle when operating, said spindle having a spindlebody provided with an axial bore, a bearing member for said spindlebody, and a rod disposed within said bore, said rod consisting ofsubstantially nonexpansible material, said bore being provided with athrust surface disposed in proximity to said transverse plane andbearing against one end of said rod, the other end of the rod abuttingagainst said bearing member.

2. A machine-tool spindle having a nose portion and a body portion, saidspindle being provided with an axial bore, a bearing member for saidbody portion, a rod disposed within said bore, said rod consisting ofsubstantially nonexpansible material, said bore being provided with athrust surface situated in the region of the nose portion of the spindleand bearing against one end of said rod, and an adjustable abutmentcarried by said bearing member and bearing against the other end of saidrod.

3. A machine-tool spindle as defined in claim 2, wherein the end of saidrod bearing against the adjustable abutment is formed by a distinctpiece of'hard material.

4. A machine-tool spindle having a portion thereof remaining in aconstant transverse plane irrespective of thermal expansion due toheating of the spindle during operation, said spindle being providedwith a spindle body provided with an axial bore, a bearing member forsaid spindle body, a rod disposed within said bore, said rod consistingof substantially nonexpansible material, an axially adjustable thrustsurface situated within said bore in proximity to said transverse planeand bearing against one end of said rod, and an axially adjustableabutment carried by said bearing member and bearing against the otherend of said rod.

FERNAND TURRE'I'I'INI.

